Why do we need an extra chip (U4) to generate the timing for Morse dots and so on? Why not use the microcontrollers internal timers?
That’s a good point. The reason is that because of the very high crystal frequency, the internal timers cannot generate delays longer than about six seconds. If we were to make up dots and dashes by adding together these intervals, there would be unacceptable switching noise on the signal caused by the timer interrupt. At best, it causes the ARGO pictures to have ‘beads’ on the dashes, and at worst, the signal is unreadable (I know, I tried!) We still use the timer, but instead of using the crystal as reference, we use an external oscillator (U4), which drives the timer at a much lower frequency, about 64Hz. This allows the 16 bit timer to provide very clean signal generation with no switching noise, and bit times as long as 1023 seconds. Dashes are made from a single timed interval, not from three dots strung together. By the way, you could use another crystal with U4, but the lower frequency crystals necessary (such as 32.768kHz) are not very reliable with the 4060 chip, and precisio
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